Treatment of Mold and Mildew on Gypsum Board - AWCI

FROM THE FOUNDATION
<strong>Treatment</strong> <strong>of</strong> <strong>Mold</strong>
<strong>and</strong> <strong>Mildew</strong>
on Gypsum Board
J.L. Houser
Domtar Gypsum
The following article is brought to
you courtesy <strong>of</strong> the Foundation <strong>of</strong>
the Wall <strong>and</strong> Ceiling Industry.
About the Author:
James L. Houser is Director <strong>of</strong>
Technical Services for Domtar Gypsum
<strong>and</strong> has been in the gypsum industry
for 35 years. Jim currently serves as
President <strong>of</strong> the Foundation <strong>of</strong> the Wall
<strong>and</strong> Ceiling Industries <strong>and</strong> chairman <strong>of</strong>
the Gypsum Association’s Technical
Committee <strong>and</strong> vice chairman <strong>of</strong> the
AWCI Technical Subcommittee, Number
3, “Gypsum <strong>and</strong> Gypsum-Related
Products.”
He is also a member <strong>of</strong> NFPA, CSI
<strong>and</strong> ASTM <strong>and</strong> the three model code
groups ICBO, BOCA <strong>and</strong> SBCCI.
Jim resides with his wife, Harriette,
in Ann Arbor, Michigan.
Moisture is perhaps the
worst enemy <strong>of</strong> gypsum
board products. Not only
can it cause sagging ceilings, but
delamination, nail pops, discoloration,
poor working qualities <strong>and</strong> mildew all
can be attributed in whole or in part to
the devastating effects <strong>of</strong> severe or continuous
high levels <strong>of</strong> moisture.
In today’s construction climate, there
is a tendency to push jobs beyond their
normal sequence schedule. Many
general contractors are willing to take
that “calculated risk” to proceed before
the job is properly closed-in or dried.
Consequently, interior drywall work
frequently becomes exposed to the
elements or excessive moisture.
During progress <strong>of</strong> the job certain
conditions should be documented by
the Drywall contractor that pose a
potential for causing delayed water
related problems. Such conditions in-
1. <strong>Mildew</strong> in early stages. Often starts in
corners on ceilings or near floors.
clude unprotected shafts <strong>and</strong> ro<strong>of</strong>
vents, accidental plumbing or sprinkler
leaks <strong>and</strong> unfinished exterior wall sections
open during precipitation.
Gypsum board is remarkably resilient
to the effects <strong>of</strong> short-term dousings
when installed on sidewalls.
Sidewalls generally dry quickly <strong>and</strong>, if
the paper remains firmly bonded to the
core, the board will most likely perform
adequately. Ceilings, however, present
a different set <strong>of</strong> circumstances that are
aggravated by the horizontal orientation
<strong>of</strong> the product. Insulation (that is <strong>of</strong>ten
in place) may become soaked, heavily
weighted <strong>and</strong> trap water for an extended
period <strong>of</strong> time.
Gypsum board derives most <strong>of</strong> its
rigidity from the tensile strength <strong>of</strong> its
surfacing papers. Severe or prolonged
exposure to moisture will cause the
paper fiber to relax or exp<strong>and</strong> <strong>and</strong> a
permanent deformation (sag) will occur
when the area dries.
There is little that can be done to correct
a set-sag in a ceiling other than installing
another layer under the sag or
replacing the ceilings with new
products.
One <strong>of</strong> the most perplexing problems
to deal with is the growth <strong>of</strong> mold <strong>and</strong>
mildew under various moisture conditions.
It is much easier to prevent than
to cure once you have been plagued
with its presence.
<strong>Mold</strong> <strong>and</strong> mildew usually occur in
areas <strong>of</strong> extended dampness, moisture
migration, poor air circulation <strong>and</strong>
temperatures above 65 degrees
Fahrenheit.
continued on page 33
Construction Dimensions/January 1989 15

Continued from page 15
are not satisfactory, gradually increase
the concentration <strong>of</strong> vinegar up to full
strength if necessary. If solution works,
a spray applicator may be used to cover
large areas.
Caution: Wear rubber gloves. . .even
vinegar can be an irritant to the skin.
There are other commercial products
on the market. “Tilex” or “Clorox”
type bleaches will work; however,
sodium hypo-chlorites are extremely
caustic <strong>and</strong> not recommended, especially
in closed areas.
The final step is to again thoroughly
dry the area <strong>and</strong> apply a roller coat <strong>of</strong>
white shellac or a quality primer/sealer
to ensure against the possibility <strong>of</strong>
bleed-through in subsequent finishes.
Don’t be misled about vinyl wallcoverings
(mildew has been known to eventually
show right through). Contaminated
wallcovering adhesives
2. Untreated growth has come through
two coats <strong>of</strong> latex paint.
<strong>Mold</strong> <strong>and</strong> mildew are caused by
fungus spores naturally occurring in the
air. The presence may be indicated by
a myriad <strong>of</strong> small spotty patches in colors
<strong>of</strong> greyish-green to black. Growth
<strong>of</strong> mold <strong>and</strong> mildew usually begins in
smaller rooms or comer areas. See picture
#1.
If left untreated, the patches will continue
to grow <strong>and</strong> intensify. Deterioration
<strong>of</strong> the paper surface may occur as
the fungus feeds on the cellulose fiber
<strong>and</strong> organic binders. See picture #3.
The first step in the treatment <strong>of</strong> the
area is to eliminate or substantially
reduce the source <strong>of</strong> the moisture to a
normal ambient level. Next, thoroughly
dry the affected area with forced air
<strong>and</strong> heat, if necessary. Then wipe the
surface growth <strong>of</strong>f with a clean dry
cloth. A terrycloth towel works well.
The next step may require some experimentation.
Recommend starting
with a solution <strong>of</strong> 40% white vinegar
in water (about six 8 oz. cups in a
gallon container then fill with clean
water). This should kill the fungus.
“TSP” or Trisodium phosphate, used
in a saturated solution, is another good
<strong>and</strong> rather inexpensive compound
which is usually effective.
Try a small test section first to see if
the remainder <strong>of</strong> the spots disappear.
Apply the solution lightly with a sponge
but do not scrub back <strong>and</strong> forth in the
same area as the paper could become
roughened or damaged. If the results
Construction Dimensions/January 1989 33

(pastes) are another source in which
mold can originate.
Prevention <strong>of</strong> mold <strong>and</strong> mildew is
relatively easy with a few common
sense precautions.
3. Severe deterioration in process.
4. Note sagging gypsum board ceiling
from moisture saturation.
1. Keep the gypsum board dry.
Comment: Job site storage should
always be <strong>of</strong>f the floor on sleuters or
risers <strong>and</strong> away from direct weather exposure
or protected with tarps.
2. Keep the installed areas dry <strong>and</strong>
ventilated. Comment: Stagnant air,
warm, moist, darkened conditions are
a perfect environment for mold <strong>and</strong>
mildew to grow.
3. Prevent wicking. comment: Gyp
sum should not be installed resting
directly on the floor. A ¼-inch space
at the floor line will usually eliminate
the potential for water wicking into the
panel.
4. A special precaution should be
observed where gypsum panels are in
direct contact with masonry or concrete
walls. Vinyl wallcoverings can trap
moisture <strong>and</strong> many adhesives are
organic based. Be certain such walls are
above grade, sufficiently cured,
thoroughly dried <strong>and</strong> properly insulated
<strong>and</strong> sealed.
5. Inspect your completed work
areas frequently. Comment: It will take
several days for mold <strong>and</strong> mildew to
develop. The sooner it is recognized <strong>and</strong>
a cure commenced, the easier it will be.
The chance <strong>of</strong> reoccurrence will also be
lessened.
Many manufacturers today use
chemical inhibitors in their papermaking
process. This helps, but isn’t
total insurance against extreme <strong>and</strong>
continuous moisture conditions that occur
more <strong>of</strong>ten than one would like.
<strong>Mold</strong> <strong>and</strong> mildew can be corrected
<strong>and</strong> treated for long term performance
without reoccurrence. The treatment is
certainly more costly than prevention
<strong>and</strong> the delay in job progress <strong>of</strong>ten
more costly than both.
The always potential presence <strong>of</strong>
mold <strong>and</strong> mildew is a classic example
<strong>of</strong> that old adage “an ounce <strong>of</strong> prevention
is worth a pound <strong>of</strong> cure.”
The Foundation <strong>of</strong> the Wall <strong>and</strong>
Ceiling Industry is a non-pr<strong>of</strong>it
organization whose sole purpose is
the improvement <strong>of</strong> the wall <strong>and</strong>
ceiling industry through reference
<strong>and</strong> research services.
The Foundation has established
<strong>and</strong> maintains the John H. Hampshire
Memorial Research <strong>and</strong>
Reference Library Library
materials—including building codes,
industry periodicals, <strong>and</strong> audio-visual
materials—are available on a free
30-day loan basis.